Explosive opening of metal diaphragms



Aug. 27, 1968 R A, MONTGOMERY ET AL 3,398,571

EXPLOSIVE OPENING OF METAL DIAPHRAGMS Filed Nov. 26, 1965 2 Sheet-Sheet 1 FIG. 2B

PROPORTIONAL Rayney A. Manfigomary Eari E. Kifimer Jam H. Abe

- INVENTORS 1968 R. A. MON TGOMERY ET AL 3,398,571

EXPLOSIVE OPENING OF METAL DIAPHRAGMS Filed Nov. 26, 1965 2 Sheets-Sheet 2 Rayner A. Monfgomavy FIG. 5 535;; %.1Z2?

nwmoRs ATTORNEY United States Patent EXPLOSIVE OPENING OF METAL DIAPHRAGMS Rayner A. Montgomery, Silver Spring, Earl E. Kilmer,

College Park, and John H. Abell, Bowie, Md., assignors to the United States of America as represented by the Secretary of the Navy Filed Nov. 26, 1965, Ser. No. 510,456 6 Claims. (Cl. 73-12) ABSTRACT OF THE DISCLOSURE A ballistics range shock tube having an explosive rupturable metal diaphragm holding the high pressure section of the shock tube closed until an aerodynamic model is fired into the ballistics range section of the shock tube, whereupon a sensing and timing device initiates the rupture of the diaphragm causing a high pressure shock wave to travel toward the model creating interaction effects between the model and the high speed shock wave air flow.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to metal diaphragms and more particularly to the explosive opening of metal diaphragms in firing a cold driver shock tube.

The shock tube is a device used to produce a shock wave which in turn produces high temperature high velocity flow. A shock tube essentially consists of a high pressure section and a low pressure section separated by a diaphragm. The high pressure section may contain either a hot (explosive gas mixture) or a cold driver gas. The shock tube may be combined either with a wind tunnel for the study of stationary models or with a ballistics range for the study of models in free flight. This latter combination is used to study the interaction of a last wave and an aerodynamic model in supersonic flight. For the study of aerodynamic models in flight a model is launched from a powder gun and propelled through a ballistics range tube toward the low pressure section of the shock tube. The diaphragm in the shock tube is ruptured causing a shock wave to travel toward the approaching model. Cameras and transducer arrangements record the shock wave and model interaction effects when the model meets the high speed air flow.

In the past when metal diaphragms have been used in shock tubes, the diaphragm has been ruptured either by increasing the presence in the high pressure section until the diaphragm bursts or mechanically piercing the diaphragm with electromechanical rupturing means. Normally if the increased pressure method were used grooves were cut in the metal diaphragm to weaken it along predetermined parting lines. The depth of these grooves being such that, theoretically, the diaphragm would rupture when the desired pressure had been attained in the explosive chamber. Certain disadvantages arise however since it has been found that diaphragms rarely rupture at precisely the desired theoretical pressure. Mechanically piercing the diaphragm has also been less than satisfactory in shock interaction studies. When shock interaction is provided the model flight time in the test section is relatively short; therefore, the opening of the diaphragm must be carefully timed so that the "ice shock wave and the model meet in the test section. Firing a cold driver shock tube with either of the aforementioned methods has not been entirely satisfactory because of the requirement of fast diaphragm opening time.

The general purpose of this invention is to provide a shock tube firing device which embraces all the advantages of similarly employed shock tube devices and possess none of the aforedescribed disadvantages. T0 attain this the present invention contemplates installing in a shock tube a metal diaphragm having precut grooves on the high pressure side of the diaphragm with explosive material lined therein. The diaphragm is prebulged to near bursting pressure and upon initiation of the explosive material releases the high pressure fluid into the low pressure section of the shock tube. When a model is launched into the evacuated range tube sensing elements therein detect the model and send an electric signal through a proportional timing device to the ex plosive diaphragm causing it to rupture at the appropriate time so that the model and the shock wave meet in the test section of the shock tube.

It is an object to provide means for firing a cold driver shock tube which is reliable and accurately time controlled.

Another object is the provision of an explosive metal diaphragm for initially separating the high pressure section of a shock tube from the low pressure test section whereby upon initiation of the explosive diaphragm, it uniformly opens and permits a shock wave to flow into the low-pressure section of the shock tube.

Still another object is the provision of an explosive metal diaphragm in a shock tube which can be initiated accurately and reliably for ballistic shock interaction pattern studies.

Yet another object is to provide an explosive metal diaphragm which can be ruptured uniformly at a precise predetermined time enabling the flow of a fluid from a high pressure chamber, which ruptures along predetermined lines to permit uniform flow of the fluid therethrough, and which is initiated from the high pressure side of said metal diaphragm.

Also it is an object to provide a shock tube testing device which is controlled by a ballistic model launched through the range tube section to precisely initiate a rupturable diaphragm so that a shock wave from the driver section of a shock tube will meet the model in the low pressure section of the shock tube.

Other objects and features of the invention will become more fully apparent as the disclosure is made of an embodiment of the invention as illustrated in the accompanying sheets of drawings in which:

FIG. 1 is an illustration of the shock tube assembly of the invention;

FIG. 2(a) is an enlarged view of the diaphragm section of the invention;

FIG. 2(b) is a side view of FIG. 2(a);

FIG. 3 is a perspective view of the high pressure side of the diaphragm in FIGS. 1 and 2 and illustrate the machined grooves with explosive material lined therein;

FIG. 4 is a perspective view of the diaphragm of the invention and illustrates the configuration thereof after rupture; and

FIG. 5 is a graph illustrating the shock interaction timing cycle.

Referring now to the drawings, wherein like numerals of reference designate like parts throughout the several views, FIG. 1 shows a model 21 being launched from a gun 23 into the evacuated range tube or housing 17. The model 21 after passing through range tube 17 travels down the test section 14 of the shock tube comprising housings 11 and 14 and a metal diaphragm 12. When the model 21 enters tube 17 after leaving gun barrel 22, sensin-g elements 18 and 19 which may be photo cells or the like detect model 21 with light screens 25 and 26 and send electrical signals over leads to proportional timer 24. Proportional timer 24 determines the velocity of the model 21 and delays sending a signal over lead 16 for a predetermined time which will enable a shock wave from driver chamber 11 to meet model 21 in a desired area of the tube 14. A signal over lead 16 is then transmitted to diaphragm explosive charge 13 which when detonated ruptures the diaphragm 12 and causes a shock wave formed by driver gas in housing 11 to travel toward the approaching model.

For ballistic studies of the interaction of the shock wave and model, windows (not shown) may be cut in the side of tube 14 and cameras, transducers, etc. (not shown), may be set up to record interaction patterns in the shock tube. Area 28 for example may be the desired area for study of interaction patterns. Discussion of the timing cycle which provides the desired interaction will be made later with reference to FIG. 5. After traveling through tube 14, model 21 passes through the open diaphragm 12 and housing 11 and terminates in a sand butt 29.

FIG. 2(a) shows a detonator cap 37 attached to base 41 which is secured to diaphragm holder 34. The end 15 of driver housing 11 illustrated in FIG. 2(b) is mounted onto diaphragm holder 34 and shock tube 14. Diaphragm 12 shown in a prebulged condition in FIG. 2(b) is connected between the two sections of diaphragm holder 34 and is sealed with gaskets 36. Precut grooves in the diaphragm 12 have an explosive charge 13 cemented in the area near the center of the diaphragm.

In the cruciform assembly shown in FIG. 2(b) an explosive lead 32 extends from the center point 31 to a detonator 43 mounted on mitigating plate 42 encapsulated by detonator block 38. Detonator 43 is sealed in block 38 with epoxy resin and is connected to lead 16 which extends through cap 37.

Diaphragm 12 is prebulged to near bursting pressure to provide more uniform opening characteristics and to prevent breaking of the bond between the cemented explosive 13 and diaphragm 12 during a pressure build-up in the high pressure section. When detonator 43 is initiated explosive lead 32 propagates to material 31 rupturing the diaphragm and permitting cold driver gas to flow down shock tube 14 in the direction indicated.

FIG. 3 shows the high pressure side of the diaphragmthe grooves in the concave surface of the diaphragm. FIG.

4 gives a perspective view of the diaphragm when opened. It shows petals 20 spread open so that cold driver gas can pass into the shock tube.

FIG. 5 is the shock interaction timing cycle for the ballistic testing device discussed in FIG. 1. At the beginning of a test a model is at position L As the model travels through the range tube, time increases from O to T and during this time detectors provide velocity information to a proportional timer. At time T and when the model is at position L indicated at point 51 on the graph, the timer sends a signal to the explosive detonator which initiates the diaphragm at almost the same time (T +At) As the shock wave then travels from position L, the model is still traveling in the opposite direction. Numeral 52 designates the point in time and space (T L where the I tages of a quick opening valve arrangement using explosive materials in other than shock tube devices may be readily appreciated by those skilled in the art.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is: 1. A cold driver shock tube firing apparatus for provid ing a shock wave in the lower pressure section of the shock tube comprising'a shock tube having a high pressure driver ehambena low pressure chamber, and

a metal diaphragm prebulged having co'ncave'and convex surfaces with said concave surface in fluid sealing relationship with the driver chamber of said shock tube, said convex surface in fluid sealing relationship with said low pressure chamber of said shock tube,

explosive means attached to said concave surface,

means connected to said explosive means fordetonating said explosive means after a predetermined-.time delay, and

proportional timing means electrically connected to said detonating means providing an electrical signal to said detonating means after said predetermined time delay.

2. The apparatus of claim 1 further comprising timer starting means connected to said timing means responsive to a detection signal to start said timer, and

said proportional timer means having delay means responsive to said detection signal to delay said detonating signal a predetermined length of time.

3. The apparatus of claim 1 further comprising a ballistics range coupled to said low pressure chamber and sensing means connected to said proportional timer for detecting the presence of an aerodynamic model in flight through said ballistics range, and said proportional timer responsive to a signal from said sensing means for providing said predetermined time delay in accordance with the velocity of said model, and

whereby a shock wave flows into the low pressure sector of the shock tube from said drive chamber after said predetermined time delay and meets said model a predetermined time later than said first time at a predetermined location in the shock tube. V

4. The apparatus of claim 1 wherein said diaphragm has grooves precut in said concave surface and said explosive means is cemented into said grooves.

5. The. apparatus of claim 4 further comprising delay means in said proportional timer for providing said predetermined timedelay sensing means connected to said proportional timer for detecting the presence of said model in flight through said ballistics range, and said proportional timer responsive to a signal from said sensing means for providing said predetermined time delay in accordance with the velocity of said model, and

whereby a shock wave flows into the low pressure sector of the shock tube from said drive chamber after said predetermined time delay and meets saidmodel a predetermined time later than said first time at predetermined location in the shock tube.

6. A shock tube assembly for testing interaction effects of a shock Wave on an aerodynamic missile in flight comprising a high pressure driver chamber, a low pressure shock tube chamber, a ballistics range chamber coupled to said low pressure chamber, a means for propelling said missile through said range and shock tube chambers, I a prebulged metal diaphragm in fluid sealing relationship between said driver and shock tube chambers, explosive means attached to one surface of saiddiaphragm, means for detonating said explosive means rupturing said diaphragm and releasing a shock wave from the driver chamber into the shock tube chamber in response to an initiation signal, and

proportional timing means determining the velocity of said missile during flight through said range chamber for providing a velocity proportional time delayed initiation signal to said detonating means whereby said shock wave and said missile meet at a predetermined position in said shock tube.

References Cited UNITED STATES PATENTS Mullaney et a1 73-12 XR Fike et a1 220-47 =Kilmer et a1 73-12 XR Escallier et al 73-12 DAVID SCHONBERG, Primary Examiner. 

